Peter Mitchell, the man who discovered the chemiosmotic energy transduction mechanism. 

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... Keilin's discovery, Peter Mitchell ( Fig. 5) pro- posed the chemiosmotic theory to explain the mecha- nism used by mitochondria to synthesize ATP (15). Ac- cording to this theory, the energy derived from the flux of electrons through the cytochrome chain is used to ex- clude protons from the inner membrane into the space available between the two mitochondrial membranes, thus generating a proton gradient across the inner mito- chondrial membrane and the matrix (electric and os- motic energies). The H gradient is then dissipated through the mitochondrial F 1 F 0 -ATP synthase, a com- plex enzyme that has several subunits, with some em- bedded into the inner membrane and others protruding from the inner mitochondrial membrane and facing the matrix. During the H efflux through the F 1 F 0 complex, the energy derived from the gradient is converted into chemical energy to synthesize ATP from ADP and P i ...

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... medium but in a theoretical condition in which the solvent would not bind to the reactants. The values found were quite different from those measured in water, thus supporting the proposal of George et al. (39). Accord- ing to these calculations, the energy of hydrolysis of an acyl phosphate residue solvated in water would be in the range of 8 to 10 kcal/mol but increased to 5 to 32.5 kcal/ mol in the gas phase. We then reasoned that the interac- tion of water with the reactant should decrease if we decreased the water activity of the solvent, thus mimicking the gas phase. We then raised the possibility that in the E 2 conformation, the catalytic site of the enzyme would be hydrophobic and that the solvation of both P i and the aspartate residue would decrease to a point that phos- phorylation would occur spontaneously (E 2 -P). In this case, the major thermodynamic barrier for the formation of the acyl phosphate residue would be not the formation of the covalent bond (Fig. 9A, reaction 5) but the binding of P i to the enzyme, i.e. the partitioning of a hydrophilic ion (P i ) from the aqueous assay medium into the hydrophobic environment of the catalytic site. Factors facilitating this partition should also facilitate the phosphorylation of the enzyme by P i . The phosphoenzyme E 2 -P formed from P i would not be able to transfer its phosphate to ADP because of the large difference in the energies of hydrolysis of the acyl phosphate in a hydrophobic environment and ATP in an aqueous solution. The binding of Ca 2 to the low-affinity site of the enzyme would then promote a con- formational change in the protein that would allow the entry of water into the catalytic site with the subsequent solvation of both the acyl phosphate residue and ADP. As a result, the energy values for the hydrolysis of the acyl phosphate and ATP would become equally high, and ATP synthesis would proceed spontaneously. Experimental conditions that reduce the entry of water into the catalytic site should also impede the synthesis of ATP. According to this hypothesis, the existence of high-and low-energy forms of the phosphoenzyme would be related solely to the water activity in the catalytic site. We tested this hypothesis by measuring the phosphorylation of the enzyme by P i and the synthesis of ATP in the presence of water and various concentrations of nondenaturing organic solvents such as dimethyl sulfoxide, glycerol, and N,N-dimethylformamide (34,(41)(42)(43). In aqueous mix- tures, these solvents markedly increase the partition coef- ficient of P i from the aqueous medium into an organic phase containing isobutyl alcohol and benzene. In previ- ous studies, we observed that in the absence of a gradient, the phosphorylation of E 2 by P i demonstrated a saturation behavior (24, 25, 31, 35), indicating the occurrence of a phosphate-enzyme complex prior to the phosphorylation reaction (Reaction ...

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... had the good fortune to be invited by Peter Mitchell (Fig. 5) for a three-day sojourn to his laboratory at the Glynn Research Centre near Bodmin, Cornwall, United Kingdom. This was an exciting adventure. When I took the train from London, I was expecting to find a tall building crowded with all sorts of laboratories. Instead, the train stopped in a small station in the countryside. The crowded building I had imagined was in fact a lovely mansion located on a farm with a small lake, cows, ducks, and everything else required for a peaceful and in- spiring environment. The research team was restricted to a staff of three: his colleague, Jennifer Moyle; a secre- tary; and another woman who took care of a rich library. At that time, there was no internet, and we had to go to printed journals to collect information. Peter was waiting for me at the entrance of the mansion and took me di- rectly to his laboratory. The first thing he showed me was a world map full of pins. Red pins located research groups that criticized his theory, white were neutral, and green supported the chemiosmotic theory. I had three lovely days of friendly discussion. On the train back to London, I could not remember clearly what specific top- ics we had discussed, but I knew that my way of thinking about energy interconversion had changed for the ...